漓江上游山区复杂地形水热通量的时空变化规律

为了估算漓江上游农林经济的发展对决定地表微气候环境的水热通量的影响,计算山区复杂地形影响下的地表太阳辐射以改进SEBAL模型,提出归一化水热通量使不同时相具有可比性,对漓江上游1989-2006年5景TM/ETM卫星图像利用改进模型反演水热通量。结果表明,在空间上随植被覆盖度的增加,显热通量降低而潜热通量增加,植被覆盖度在0.2～0.7时的影响非常显著。1989-2000年植被覆盖度均值明显降低,而2000-2006年逐渐上升,导致波文比(显热与潜热比)均值明显升高然后逐渐降低,归一化潜热数值较高的像元比例减少然后增加,归一化显热数值较高的像元比例增加然后减少。尽管在2006年植被覆盖度均值接近于1989年,但波文比均值仍明显高于1989年。研究区经济林、旱地农作物面积的增加,阔叶林面积减少,水源林的减少与退化,导致了显热与潜热比平均值的升高。

Spatio-temporal variation of water and heat fluxes over complex hilly topography in upper reaches of Lijiang river

Land surface water and heat fluxes are the main factors affecting local microclimate. In order to evaluate the impact of agricultural and forest economical development of the upper reaches of Lijiang river on environment, the fluxes were retrieved with improved SEBAL model from five TM/ETM images of the upper reaches of Lijiang river during 1989 to 2006 by computation of surface solar radiation in complex hilly topography. Normalized water and heat fluxes were proposed so that they could be compared between different temporal domains. Results showed that while vegetation coverage increased, sensible heat flux(H) decreased and latent heat flux(LE) increased. The influence was very obvious while vegetation coverage ranged from 0.2 to 0.7. Average vegetation coverage decreased sharply from 1989 to 1991, and increased gradually from 2000 to 2006. It respectively resulted in great enhancement and then gradually fall in average Bowen ratio (ratio of H to LE) and in pixels with higher normalized sensible heat flux, as well as proportional fall and then rise in pixels with higher normalized latent heat flux. Although average vegetation coverage in 2006 approached that in 1989, average Bowen ratio was still greater than that in 1989. The enhancement of average ratio of sensible heat flux to latent heat flux results from the increase of economical forests and agricultural dry land, the decrease of broadleaf forest coverage, and the shrinkage and degradation of water source forest in the study area.